Stable well cementing methods and compositions

ABSTRACT

The present invention provides stable well cementing methods and compositions for sealing subterranean zones penetrated by well bores. The improved thermally stable and degradation resistant well cement compositions are basically comprised of a hydraulic cement, sufficient water to form a pumpable slurry, an aqueous hydrogenated styrene-butadiene rubber latex and a latex stabilizer present in an amount sufficient to stabilize the hydrogenated styrene-butadiene latex.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 10/201,171,filed Jul. 23, 2002, now U.S. Pat. No. 6,516,884.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to stable well cementing methods andcompositions, and more particularly, to such methods and well cementcompositions which are thermally stable and degradation resistant.

2. Description of the Prior Art

Hydraulic cement compositions are commonly utilized in oil, gas andwater well completion and remedial operations. For example, hydrauliccement compositions are used in primary cementing operations wherebystrings of pipe such as casings and liners are cemented in well bores.In performing primary cementing, a hydraulic cement composition ispumped into the annular space between the walls of a well bore and theexterior surfaces of a string of pipe disposed therein. The cementcomposition is permitted to set in the annular space thereby forming anannular sheath of hardened, substantially impermeable cement therein.The cement sheath physically supports and positions the pipe in the wellbore and bonds the pipe to the walls of the well, bore whereby theundesirable migration of fluids between zones or formations penetratedby the well bore is prevented.

When conventional cement compositions are utilized for sealing pipestrings in well bores or for carrying out other remedial or repairprocedures in high temperature wells including geothermal wells, theconventional cement compositions are unstable after setting due tosettling of the particulate solids in the cement composition and sufferfrom strength degradation due to exposure to the high temperatures,corrosion and the like.

Thus, there are needs for improved cementing methods and compositionswhich are thermally stable and degradation resistant.

SUMMARY OF THE INVENTION

The present invention provides improved methods of sealing subterraneanzones penetrated by well bores and improved thermally stable anddegradation resistant well cement compositions which meet the abovedescribed needs and overcome the deficiencies of the prior art. Themethods of the present invention basically comprise the following steps.An improved thermally stable and degradation resistant cementcomposition is provided comprised of a hydraulic cement, sufficientwater to form a pumpable slurry, an aqueous hydrogenatedstyrene-butadiene rubber latex and a latex stabilizer present in anamount sufficient to stabilize the hydrogenated styrene-butadiene latex.The cement composition is placed in a subterranean zone to be cementedand thereafter, the cement composition is allowed to set into a hard,impermeable, thermally stable and degradation resistant mass.

The improved thermally stable and degradation resistant well cementcompositions of this invention are basically comprised of a hydrauliccement, sufficient water to form a pumpable slurry, an aqueoushydrogenated styrene-butadiene rubber latex and a latex stabilizerpresent in an amount sufficient to stabilize the hydrogenatedstyrene-butadiene latex.

The hydrogenated styrene-butadiene rubber utilized in the aqueous latexthereof has in the range of from about 80% to about 95% of the availablecarbon valence bonds attached to separate other atoms. The weight ratioof styrene to butadiene in the hydrogenated styrene-butadiene rubber isin the range of from about 5:95 to about 95:5. The presence of thehydrogenated styrene-butadiene rubber in the cement composition providesimproved thermal stability at high temperatures as well as improvedstrength and corrosion degradation resistance at high temperatures.

The objects, features and advantages of the present invention will beapparent to those skilled in the art upon a reading of the descriptionof preferred embodiments which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the reduction of styrene-butadiene rubber by observation ofthe percent transmittance of the carbon-carbon double bonds.

FIG. 2 shows the onset of thermal degradation of styrene-butadienerubber and hydrogenated (reduced) styrene-butadiene rubber.

FIG. 3 shows a scanning electron microscope photograph of crushed setcement containing hydrogenated styrene-butadiene rubber.

FIG. 4 shows a scanning electron microscope photograph of crushed cementcontaining styrene-butadiene rubber.

DESCRIPTION OF PREFERRED EMBODIMENTS

Improved methods for sealing subterranean zones penetrated by well boreshaving high temperatures, i.e., temperatures up to and including 700°F., are provided by the present invention. The methods utilize improvedthermally stable and degradation resistant cement compositions forsealing the subterranean zones. In accordance with the methods, animproved thermally stable and degradation resistant cement compositionof this invention is provided, the cement composition is placed in thesubterranean zone to be sealed and the cement composition is allowed toset into a hard impermeable mass therein.

The improved thermally stable and degradation resistant cementcompositions of this invention are basically comprised of a hydrauliccement, sufficient water to form a pumpable slurry, an aqueoushydrogenated styrene-butadiene rubber latex and a latex stabilizerpresent in an amount sufficient to stabilize the hydrogenatedstyrene-butadiene latex.

Aqueous lattices of styrene-butadiene rubber and latex stabilizers haveheretofore been utilized in well cement compositions to cause quicksetting of the cement compositions and to inhibit pressurized formationfluid channeling in the cement compositions. As described furtherhereinbelow, the present invention utilizes an aqueous latex ofhydrogenated styrene-butadiene rubber with a latex stabilizer to providevery high temperature stability to a well cement composition, i.e.,stability at temperatures in the range of from about 80° F. to about700° F. The cement compositions of this invention also have excellentstrength and corrosion degradation resistance at high temperatureswhereby they are suitable for use in high temperature wells includinggeothermal wells.

A variety of hydraulic cements can be utilized in accordance with thepresent invention including those comprised of calcium, aluminum,silicon, oxygen and/or sulfur which set and harden by reaction withwater. Such hydraulic cements include Portland cements, slag cements,pozzolana cements, gypsum cements, aluminous cements and silica cements.Portland cements or their equivalents are generally preferred for use inaccordance with the present invention. Portland cements of the typesdefined and described in the API Specification For Materials And TestingFor Well Cements, API Specification 10, 5^(th) Edition, dated Jul. 1,1990 of the American Petroleum Institute are particularly suitable.Preferred such API Portland cements include classes A, B, C, G and H,with API classes G and H being preferred.

The water utilized to form the cement compositions of this invention canbe fresh water, unsaturated salt solutions or saturated salt solutionsincluding brine and seawater.

Generally, water from any source can be utilized so long as it doesn'tadversely react with components of the cement compositions. The water isgenerally included in the cement compositions of this invention in anamount in the range of from about 35% to about 60% by weight ofhydraulic cement therein.

The aqueous hydrogenated styrene-butadiene rubber latex utilized inaccordance with this invention is included in the cement composition ina general amount in the range of from about 8% to about 52% by weight ofhydraulic cement in the composition, more preferably in an amount offrom about 17% to about 26% by weight of hydraulic cement.

The hydrogenated styrene-butadiene rubber in the aqueous latex has inthe range of from about 80% to about 95% of the available carbon atomvalence bonds attached to separate other atoms, more preferably, thehydrogenated styrene-butadiene rubber has in the range of from about 90%to about 95% of the available carbon atom valence bonds attached toseparate other atoms. The weight ratio of styrene to butadiene in thehydrogenated styrene-butadiene rubber is preferably in the range of fromabout 5:95 to about 95:5. The most preferred hydrogenatedstyrene-butadiene rubber has a weight ratio of styrene to butadiene ofabout 30:70. The hydrogenated styrene-butadiene rubber is present in theaqueous latex thereof in an amount in the range of from about 25% toabout 75% by weight of the aqueous latex, more preferably in an amountof from about 30% to about 70%.

In order to prevent the aqueous rubber latex from prematurelycoagulating and increasing the viscosity of the cement compositions, aneffective amount of a latex stabilizer is included in the cementcompositions. Latex stabilizers are comprised of one or more surfactantswhich function to prevent latex coagulation. Examples of rubber latexstabilizing surfactants which can be utilized in the cement compositionsinclude, but are not limited to, surfactants having the formulaR—Ph—O(OCH₂CH₂)_(m)OH wherein R is an alkyl group having from about 5 toabout 30 carbon atoms, Ph is phenyl and m is an integer of from about 5to about 50 and surfactants having the formula R₁(R₂O)_(n)SO₃X whereinR₁ is an alkyl group having from about 5 to about 20 carbon atoms, R₂ isthe group —CH₂—CH₂—, n is an integer from about 10 to about 40 and X isa cation. Of the various latex stabilizing surfactants which can beutilized, a sodium salt of an ethoxylated (15 moles or 40 moles) C₁₅alcohol sulfonate having the formula H(CH₂)₁₅(CH₂CH₂O)₁₅SO₃Na ispreferred. The rubber latex stabilizing surfactant utilized is includedin the cement composition in an amount in the range of from about 10% toabout 25% by volume of the aqueous rubber latex therein, more preferablyin an amount of about 15%.

As is well understood by those skilled in the art, a variety of cementcomposition additives can be included in the cement compositions of thisinvention including, but not limited to, defoamers, set retarders,dispersants, strength retrogression preventing materials, weightingmaterials, suspending agents and the like.

As mentioned above, the improved thermally stable and degradationresistant well cement compositions of this invention are basicallycomprised of a hydraulic cement, sufficient water to form a pumpableslurry, an aqueous hydrogenated styrene-butadiene rubber latex and alatex stabilizer present in an amount sufficient to stabilize thehydrogenated styrene-butadiene latex. The aqueous hydrogenatedstyrene-butadiene rubber latex provides high thermal stability to thecement compositions, i.e., the cement compositions set at temperaturesas high as 700° F. and remain stable and strength and corrosiondegradation resistant at such temperatures. In addition, the presence ofthe aqueous hydrogenated styrene-butadiene rubber latex prevents fluidloss from the cement compositions prior to setting and forms a rubberlayer on the surfaces of the cement compositions after setting whichcontributes to the prevention of strength and corrosion degradation.

A preferred method of the present invention for sealing a subterraneanzone penetrated by a well bore is comprised of the steps of: (a)providing an improved thermally stable and degradation resistant cementcomposition comprised of Portland cement, sufficient water to form apumpable slurry, an aqueous hydrogenated styrene-butadiene rubber latexpresent in an amount in the range of from about 8% to about 52% byweight of hydraulic cement in the composition and a latex stabilizerpresent in an amount sufficient to stabilize the hydrogenatedstyrene-butadiene latex; (b) placing the cement composition in thesubterranean zone; and (c) allowing the cement composition to set into ahard impermeable mass.

Another preferred method of this invention for sealing a subterraneanzone penetrated by a well bore comprises the steps of: (a) providing animproved thermally stable and degradation resistant cement compositioncomprised of Portland cement, sufficient water to form a pumpableslurry, an aqueous hydrogenated styrene-butadiene rubber latexcontaining styrene-butadiene rubber having in the range of from about80% to about 95% of the available carbon atom valence bonds attached toseparate other atoms present in the cement composition in an amount inthe range of from about 8% to about 52% by weight of hydraulic cement inthe composition and a latex stabilizer present in an amount sufficientto stabilize the hydrogenated styrene-butadiene latex; (b) placing thecement composition in the subterranean zone; and (c) allowing the cementcomposition to set into a hard impermeable mass.

A preferred improved thermally stable and degradation resistant wellcement composition comprises: Portland cement; sufficient water to forma pumpable slurry; an aqueous latex of hydrogenated styrene-butadienerubber latex present in an amount in the range of from about 8% to about52% by weight of hydraulic cement in the composition; and a latexstabilizer present in an amount sufficient to stabilize the hydrogenatedstyrene-butadiene latex.

Another preferred improved thermally stable and degradation resistantwell cement composition comprises: Portland cement; sufficient water toform a pumpable slurry; an aqueous hydrogenated styrene-butadiene rubberlatex having in the range of from about 80% to about 95% of theavailable carbon atom valence bonds attached to separate other atomspresent in an amount in the range of from about 8% to about 52% byweight of hydraulic cement in the composition; and a latex stabilizerpresent in an amount sufficient to stabilize the hydrogenatedstyrene-butadiene latex.

In order to further illustrate the methods and compositions of thisinvention, the following examples are given.

EXAMPLE I

Hydrogenated styrene-butadiene rubber (HSBR) latex was prepared usingstyrene-butadiene rubber (SBR) latex containing 25% styrene and 75%butadiene in accordance with the method described in the PolymericEncyclopedia, Vol. 3, pgs. 20-46 (1995) as follows.

To 200 grams of SBR latex (50% active) was added 1.52 moles (48.58grams) of hydrazine and 5.52×10⁻⁵ mole of copper sulfate pentahydrate(0.0138 grams). Prior to the addition of the hydrazine and coppersulfate, the pH of the SBR latex was raised to 10 by the addition ofpotassium hydroxide. The resulting mixture was heated to 131 ° F. andheld at that temperature. Once the mixture maintained a steadytemperature of 131° F., 1.52 moles (120 grams) of hydrogen peroxide wasvery slowly added to the mixture with vigorous agitation. The additionwas complete in approximately 2 hours as indicated by the lack ofevolution of nitrogen gas. The progress of the reduction (addition ofhydrogen) of the SBR latex was followed by observing the % transmittanceof the carbon-carbon double bonds at wave lengths of 966.53 cm⁻¹ and911.29 cm⁻¹ as shown in FIG. 1. The substantial decrease in double bondsshown in FIG. 1 indicate the extent of the reduction.

EXAMPLE II

Various cement compositions were prepared which included the HSBR or theSBR latexes described in Example I as well as Class H Portland cement,water and various other additives as indicated in Table I below.

TABLE I Cement Compositions Containing SBR Latex Or HSBR Latex AndAdditives Latex HSBR Strength Weighting Suspend- Water, SBR Sta- De- SetDisper- Latex⁹, Retrogression Ma- ing Compo- Portland % by Latex¹, %bilizer², foamer³, Retarder, sant⁸, % by Preventing terial¹², Agent¹³,sition Density, Cement wt. of by wt. of % by wt. % by wt. % by wt. % bywt. wt. of Material, % by % by wt. % by wt. No. lb/gal Class cementcement of cement of cement of cement of cement cement wt. of cement ofcement of cement 1 16.4 H 17.7 17.7 1.8 0.009 0.1⁴ 1.5 2 16.4 H 8 1.80.009 0.1⁴ 1.5 34 3 18.5 H 31.9 17.7 2.7 0.007 3.2⁵ 1.5 35¹¹ 60 4 18.5 H16.5 2.8 10.7⁵  1.5 27.2 35¹¹ 60 5 18.3 H 28.4 26.6 2.8 1.9⁶ & 0.8⁷17.5¹⁰ & 17.5¹¹ 60 0.5 6 18.3 H 0 5.7 1.9⁶ & 0.8⁷ 51.1 17.5¹⁰ & 17.5¹¹60 0.5 ¹SBR Latex (50% active) ²Sodium salt of ethoxylated (15 moles) ofC₁₅ alcohol sulfonate ³Silicone defoamer ⁴Sulfomethylated lignosulfonate⁵A mixture of calcium lignosulfonate and gluconic acid ⁶Tartaric acid⁷Copolymer of acrylic acid and 2-acrylamido-2-methyl propane sulfonicacid ⁸Naphthalene sulfonatc condenscd with formaldehyde ⁹HSBR Latex (25%active) ¹⁰Crystalline silica ¹¹Silica flour ¹²Iron oxide¹³Hydroxypropylguar

The fluid loss, thickening times and compressive strengths of the cementcompositions shown in Table I were determined in accordance with theabove mentioned API Specification 10. The results of the tests are givenin Tables II and III below.

TABLE II Fluid Loss And Thickening Time Test Results CompositionTemperature, Fluid Loss, Thickening Time, No. ° F. cc/30 min hr:min 1190 30 4:30 2 190 22 6:07 3 292 15 3:53 4 292 10 5:38 5 420 92 — 6 42034 —

From Table II it can be seen that the fluid loss control of the testcement compositions at bottom hole circulating temperatures ranging from80° F. to 292° F. were comparable. However, a significant departure wasnoted when the temperature was raised to 420° F. The compositioncontaining SBR latex (Composition No. 5) gave a fluid loss of 92cc/30min. as compared to the cement composition containing HSBR latex(Composition No. 6) which gave a fluid loss of 34cc/30 min. As shown inTable II, the thickening time of the various compositions werecomparable.

TABLE III Compressive Strength Test Results Composition Temperature,Curing Time, Compressive Strength, No. ° F. hours psi 3 80 72 954 4 8072 971 3 450 72 532 4 450 72 1076

From Table III it can be seen that at a curing time of 80° F., nosignificant differences in the compressive strengths of the compositionscontaining either SBR latex or HSBR latex were noted. However, at 450°F., the composition containing SBR latex had a compressive strengthwhich was approximately one-half of the compressive strength of thecomposition containing HSBR latex. This clearly indicates that thecompositions containing the HSBR latex can withstand higher temperaturesfor longer periods of time than the compositions containing the SBRlatex. That is, the composition including the HSBR latex can be utilizedat very high temperatures without fear of cement sheath failure.

EXAMPLE III

FIG. 2 shows the results of a thermogravimetric analysis of cementcompositions numbers 3 and 4 set forth in Table I above containing SBRlatex and. HSBR latex, respectively. As shown in FIG. 2, the compositioncontaining SBR latex has a higher percentage of degradation per degreeat 697° F. compared to the composition containing HSBR latex at 723° F.Thus, cement compositions containing HSBR latex are thermally morestable than cement compositions containing SBR latex and will withstandhigher temperatures.

EXAMPLE IV

The cement compositions Numbers 5 and 6 set forth in Table I abovecontaining the same concentration of SBR latex and HSBR latex,respectively, were cured at 600° F. for 7 days in an autoclave under apressure of 3,000 psi. The cured samples were crushed and examined by anenvironmental scanning electron microscope and the photographs producedare shown in FIGS. 3 and 4. The photograph of FIG. 3 is of the curedcement composition containing HSBR latex. The photograph of FIG. 4 showsthe cured cement composition containing SBR latex. As shown in FIG. 3,the crushed cement composition containing HSBR latex shows an extensiverubbery film in the composition. FIG. 4 which shows the crushed cementcomposition containing SBR latex shows a significant loss of the rubberyfilm as compared to FIG. 3.

An elemental analysis of the crushed cement compositions containing theSBR latex and HSBR latex was carried out by energy dispersive X-ray. Theresults of the analysis are shown in Table IV.

TABLE IV Elemental Analysis Of Cured Cement Compositions Containing SBRand HSBR Latexes Cement Composition No. 5 Cement Composition No. 6Containing SBR Latex, Containing HSBR Latex, Element % by Weight % byWeight Carbon 11.18 25.75 Oxygen 23.05 20.40 Aluminum 1.49 0.91 Silicon23.12 22.36 Calcium 37.93 29.28 Iron 3.23 1.30 TOTAL 100.00 100.00

As shown in Table IV, the carbon content in Composition No. 6 containingHSBR latex was 25.75% by weight as compared to an 11.8% by weight carbonin Composition No. 5 containing SBR latex. This further indicates thatcement compositions containing HSBR latex are more thermally stable thancement compositions containing SBR latex.

Thus, the present invention is well adapted to carry out the objects andadvantages mentioned as those which are inherent therein. While numerouschanges may be made by those skilled in the art, such changes areencompassed within the spirit of this invention as defined by theappended claims.

What is claimed is:
 1. A cement composition comprising: a hydrauliccement; sufficient water to form a pumpable slurry; an aqueoushydrogenated styrene-butadiene rubber latex; and a latex stabilizerpresent in an amount sufficient to stabilize said hydrogenatedstyrene-butadiene latex.
 2. The cement composition of claim 1 whereinsaid aqueous hydrogenated styrene-butadiene rubber latex is present inan amount in the range of from about 8% to about 52% by weight ofhydraulic cement in said composition.
 3. The cement composition of claim1 wherein said hydrogenated styrene-butadiene rubber in said aqueouslatex has in the range of from about 80% to about 95% of the availablecarbon atom valence bonds attached to separate other atoms.
 4. Thecement composition of claim 1 wherein the weight ratio of styrene tobutadiene in said hydrogenated styrene-butadiene rubber in said aqueouslatex is in the range of from about 5:95 to about 95:5.
 5. The cementcomposition of claim 2 wherein the weight ratio of styrene to butadienein said hydrogenated styrene-butadiene rubber in said aqueous latex isabout 30:70.
 6. The cement composition of claim 1 wherein said hydrauliccement is selected from the group consisting of Portland cements, slagcements, pozzolana cements, gypsum cements, aluminous cements and silicacements.
 7. The cement composition of claim 1 wherein said hydrauliccement is Portland cement.
 8. The cement composition of claim 1 whereinsaid water is selected from the group consisting of fresh water,unsaturated salt solutions and saturated salt solutions.
 9. The cementcomposition of claim 1 wherein said water is present in said cementcomposition in an amount in the range of from about 35% to about 60% byweight of hydraulic cement therein.
 10. The cement composition of claim1 wherein said hydrogenated styrene-butadiene rubber is present in saidaqueous latex in an amount in the range of from about 25% to about 75%by weight of said aqueous latex.
 11. The cement composition of claim 1wherein said latex stabilizer is the sodium salt of an ethoxylated C₁₅alcohol sulfonate.
 12. The cement composition of claim 1 wherein saidlatex stabilizer is present in said cement composition in an amount inthe range of from about 10% to about 25% by volume of the aqueous rubberlatex therein.
 13. A cement composition comprising: a hydraulic cement;sufficient water to form a pumpable slurry; an aqueous hydrogenatedstyrene-butadiene rubber latex having in the range of from about 80% toabout 95% of the available carbon atom valence bonds attached toseparate other atoms present in an amount in the range of from about 8%to about 52% by weight of hydraulic cement in said composition; and alatex stabilizer present in an amount sufficient to stabilize saidhydrogenated styrene-butadiene latex.
 14. The cement composition ofclaim 13 wherein the weight ratio of styrene to butadiene in saidhydrogenated styrene-butadiene rubber in said aqueous latex is in therange of from about 5:95 to about 95:5.
 15. The cement composition ofclaim 13 wherein the weight ratio of styrene to butadiene in saidhydrogenated styrene-butadiene rubber in said aqueous latex is about30:70.
 16. The cement composition of claim 13 wherein said hydrauliccement is selected from the group consisting of Portland cements, slagcements, pozzolana cements, gypsum cements, aluminous cements and silicacements.
 17. The cement composition of claim 13 wherein said hydrauliccement is Portland cement.
 18. The cement composition of claim 13wherein said water is selected from the group consisting of fresh water,unsaturated salt solutions and saturated salt solutions.
 19. The cementcomposition of claim 13 wherein said water is present in said cementcomposition in an amount in the range of from about 35% to about 60% byweight of hydraulic cement therein.
 20. The cement composition of claim13 wherein said hydrogenated styrene-butadiene rubber is present in saidaqueous latex in an amount in the range of from about 25% to about 75%by weight of said aqueous latex.
 21. The cement composition of claim 13wherein said latex stabilizer is the sodium salt of an ethoxylated C₁₅alcohol sulfonate.
 22. The cement composition of claim 13 wherein saidlatex stabilizer is present in said cement composition in an amount inthe range of from about 10% to about 25% by volume of the aqueous rubberlatex therein.